The present invention relates to a process for the removal of liquid from a solid particulate material of non-uniform particle size, the process comprising contacting the particulate material with superheated steam under non-oxidizing conditions to evaporate liquid contained in the particulate material, separating the solid material thus treated from the steam, and optionally utilizing the steam thus separated for the treatment of additional solid particulate material.
It is known to dry various organic materials by a process of the above-mentioned type. Thus, European patent application No. 82 850018.1 (Publication No. 0 058 651 A1) discloses a method of preparing cattle feed from various agricultural products, such as sugar beet pulp, molasses, citrus fruit pulp and peel and various fermentation products.
The prior art method comprises the steps of initially heating the particulate material with superheated steam and subsequently disintegrating the material to obtain a particulate material of uniform particle size. By using steam as carrier gas, the material thus formed is subsequently passed through a drier consisting of a plurality of tubular heat exchangers arranged in series and into a cyclone in which the solid material is separated and from which steam is recycled and admixed with the disintegrated material.
The purpose of disintegrating the solid particulate material before introducing it into the tubular heat exchangers is to avoid the problems associated with a material having a non-uniform particle size. Thus, such materials require tubular heat exchangers of great lengths to ensure that the largest particles have been efficiently dried when reaching the outlet end of the drier and the inlet of the cyclone. However, the disintegration is not only energy-consuming and makes the apparatus for performing the method more complicated, but the disintegration may additionally cause such changes in the character of the material that the use of the material becomes restricted. Thus, it is known that cattle feed should contain a relatively large proportion of coarse particles to ensure optimum digestion. The disintegration which serves to provide fine uniform particles has an adverse effect in this regard. Furthermore, the disintegration may cause dry material to be dusty.